Trechus quadristriatus (Schrank, 1781)

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ADEPHAGA Clairville, 1806

CARABIDAE Latreille, 1802

TRECHINAE Bonelli, 1810

TRECHINI Bonelli, 1810

Trechus Clairville, 1806

This species is native to the western Palaearctic region; it is generally common throughout Europe from the Mediterranean north to the UK and central provinces of Fennoscandia, it is present on the Mediterranean islands and Morocco and the distribution continues through Russia and Asia Minor to the Caspian Sea and Tajikistan. The earliest record from North America is from 1965, although the distribution might suggest it was introduced into the Great Lakes region beforehand, and it is now established and widespread in the north east United States and around the great Lakes. The species is common and often abundant throughout England, Wales and south-eastern Scotland, and rather less so further north to Shetland and across Ireland. Adults are present year-round; the main overwintering stage is the larva but adults live for about a year and those surviving into the autumn will go on to overwinter, they are active from April or May until late in the year and peak in abundance during August and September. Typical habitats are open and rather dry grassland, wasteland and moorland etc., especially near the coast, but they are often common in disturbed areas such as parks, domestic gardens and farmland. The species is fully winged, although seasonal changes in flight-muscle metabolism have been noted from continental specimens, and flies in the evening and at night, it is known to disperse over great distances and specimens almost certainly arrive in eastern England from mainland Europe during the summer. There seems to be no preference for substrate type but the species occurs predominantly in lowland areas, in central Europe, where it also occurs more generally in wooded areas, it occurs in mountain valleys up to 1200 m and, exceptionally, has been recorded to 2000m. Reproduction occurs in late summer and autumn although a small proportion of adults may reproduce in the spring, and eggs are laid in the soil during the autumn. Larvae overwinter in the soil, they may be active in all but the coldest periods but development continues into the spring, they feed mainly on slow-moving subterranean prey such as collembolans, worms and nematodes, but they will consume carrion which they find by chance encounter. New-generation adults appear from early spring, they are mainly terrestrial predators but will also take carrion, they are aggressive hunters and readily attack other small carabids in captivity and females will even consume their own eggs, in the field they readily consume small worms and larvae etc. and, along with the larvae, they are thought to play a role in the natural control of crop pests such as aphids and cabbage root fly (Delia radicum L.) Adults are easily found by general searching, carrion may attract them and they often occur in numbers in pitfall and flight-interception traps, in the summer they come to light (tungsten and UV) and on certain warm evenings in July or August they may arrive in very large numbers.

Trechus quadristriatus 1

Trechus quadristriatus 1

Trechus quadristriatus 2

Trechus quadristriatus 2

Trechus quadristriatus 3

Trechus quadristriatus 3

3.5-4.1 mm. Broad and flattened with a relatively large head and weakly rounded elytra, entirely pale to dark reddish-brown, often slightly iridescent, but often with the head and pronotal disc darker. Head broadest across convex and protruding eyes, temples strongly converging to a short neck, frontal furrows continued widely around the inner margin of the eyes to the temples, surface with indistinct isodiametric microsculpture (X40). Eyes with two setiferous punctures along the inner margin, the posterior of which lies about equidistant between the eye and the frontal groove. Terminal maxillary palpomere well developed; more slender but almost as long as the penultimate segment. Antennae brown, long and filiform with all segments elongate and slender. Pronotum transverse, curved and broadest anteriorly and narrowed and almost straight to obtuse posterior angles, basal margin oblique laterally, surface smooth, shiny and impressed medially. Elytra weakly curved and slightly dilated from rounded shoulders to a continuous apical margin, raised basal border (from the shoulder) abbreviated before the scutellum, usually with four well developed and finely punctured striae and several much weaker lateral striae, sutural stria recurved and deeply impressed at the apex. Elytral interstices very finely microsculptured (X40), third interstice with three setiferous punctures-these can be very difficult to see and the specimen may need to be manipulated under low angle light-the posterior puncture often lies at the apex of the third striae, always within the area bordered by the recurved sutural stria. Wings fully developed and usually visible through the elytra. Legs entirely pale brown. Front tibiae with a strong subapical notch and a single internal spur at the apex. Claws smooth. Male with two front tarsal segments dilated.

Very similar to T. obtusus Erichson, 1837 but with less curved and flatter elytra and better defined striae. In the UK the present species is always fully-winged while obtusus is always wingless. The position of the posterior supra-orbital puncture is usually diagnostic; in the present species it is placed midway between the eye and the frontal groove whereas in obtusus it is placed closer to the groove. Males can be distinguished by the form of the median lobe; in obtusus it is broader and more-or-less straight whereas in the present species it is twisted to the right (from above) before the apex.